1. Field of the Invention
This invention relates to a center pivot irrigation system having the ability to irrigate the corners of the field being irrigated and wherein the system is not equipped with sprinkler pressure regulators or sprinkler flow control devices. More particularly, this invention relates to an improved method for controlling the distribution of water from the center pivot portion of the system as the sprinklers on the corner span are sequenced.
2. Description of the Related Art
Conventional center pivot irrigation systems comprise an elongated main boom pivotally connected at its inner end to a center pivot structure and extending outwardly therefrom. The main boom of the conventional center pivot irrigation system is comprised of a plurality of pipes connected together in an end-to-end fashion which are supported upon a plurality of drive towers. In most conventional center pivot irrigation systems, the outermost drive tower or last regular drive unit (L.R.D.U.) is the master tower with the other drive towers being selectively driven in response to angular displacement of the boom section adjacent thereto.
In the early 1970s, corner systems for center pivot irrigation systems were developed to enable the corners of a square field to be irrigated. See, for example, U.S. Pat. Nos. 3,797,517; 3,802,726; and 3,902,668. Corner systems usually consist of an extension boom or arm, sometimes referred to as a corner span, which is pivotally connected to the outer end of the main boom and which is supported on at least one steerable drive tower. A guidance system is provided for guiding or steering the extension tower, and extension boom, out into the corners of the field as the main arm travels around the field.
A plurality of spaced-apart sprinklers are provided on the main boom as well as on the extension boom. Perhaps the most popular method of guiding the extension tower is the buried wire system described in U.S. Pat. No. 3,902,668. Current center pivot irrigation systems or machines equipped with a corner span will make one speed change as a plurality of sprinkler sequences are turned "on" one at a time (usually six to eight sequences) on the corner span. Those same systems usually make one speed change as a plurality of sprinkler sequences are turned "off" one at a time (usually six to eight sequences) on the corner system. In other words, the center pivot machine will usually slow down as the corner arm is extending out into the corner of the field and will speed up as the corner span is retracting from the corner of the field. The sprinklers on the corner arm are sequenced "on" as the corner arm is extending and are sequenced "off" as the corner arm is retracted. This procedure results in a large portion of the field beneath the center pivot machine being either overwatered or underwatered.